I think whole application on One screen looks very complex, many of end user have issue to find specific module/field.
Its totally depends on requirements. for example if client need one dashboard (e.g maintain status, reservation etc). then its preferable.
In real life application like business application, its better to categorize your application in modules. you may need setups for main screen. for example if you are developing for school, you need basic setups for registration, staff type, subjects offered etc.
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Solution 1 applying tab pages and panels have same idea of categorizing application. but still think about if you have more then 10 panels, then how client will handle, and how you will implement programming logic.
If you face issue in Wpf for multiple screens as (WPF provide no MDI interface by default). Here is useful link for you, in which you can implement MDI interface.
Download and enjoy MDI.
http://wpfmdi.codeplex.com/[
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